The present invention is directed to pH optrodes for sensing pH in a liquid environment, and a process for the preparation of such optrodes.
Fiber optic pH sensors have been described in the art using a variety of fluorescent dyes and techniques for immobilizing the dye at the end of the optical fiber. However, there is still a problem with regard to the sensitivity of the fluorescent spaced pH dyes which degrade and can inhibit their long-term usefulness.
U.S. Pat. No. 4,798,738 discloses a method for covalently immobilizing HPTS (hydroxypyrenetrisulfonic acid) dye in a polymer, such as cellulose, on an optical fiber by dissolving the dye-bearing polymer in a solvent and depositing the solvated dye onto the fiber. The dye-bearing polymer is regenerated as a gelatin which coats the tip of the fiber. As a coating, the amount of dye in the polymer at the fiber tip is therefore limited.
It is therefore an object of the present invention to provide pH optrodes in which the amount of fluorescent-sensitive dye seen by the optical sensor is not limited by a coating.
It is a further object of the present invention to provide a pH optrode having improved long-term stability.
It is a further object of the present invention to provide a dye-polymer matrix that is a self-contained structure and can be applied as a sensor in a variety of optical sensing formats.
These and other objects of the invention will be apparent from the following description and from the practice of the invention.